1. Technical Field
The present disclosure relates to a light emitting diode (LED) unit and, more particularly, to an LED unit comprising a transparent envelope having a favorable light-collimating capability.
2. Description of Related Art
LEDs, available since the early 1960's, has increasingly used in a variety of occasions, such as residential, traffic, commercial, and industrial, because of high light-emitting efficiency. Generally, different occasions require different illumination patterns. For example, a square may require a diffused illumination due to a large area thereof to be illuminated, and a stage may require a high-intensity illumination to be clearly presented to audience. For a road, particularly, a road for vehicle, a continuous and uniform illumination is even compellent for ensuring safe of the vehicle. Therefore, the LEDs are often arranged side-by-side in an enclosure of a lamp, thereby projecting light on the road without obvious dark spots. However, the LEDs generally cannot produce desirable light pattern by themselves due to size limitations thereof. Even after collimation by an encapsulant (often in the shape of lens) of the LED, the light output from the LED would still fall well short of such light pattern requirement.
Therefore, some optical structures are often incorporated to the lamp to adjust the light emitted from the LEDs. A most commonly used optical structure is reflector. The reflector is secured between the LEDs and the enclosure of the lamp to reflect the light emitted by the LEDs toward predetermined directions, thereby producing desirable light pattern over the road.
The reflector usually has a large volume so that all of the LEDs could be given attentions thereby. However, such a large volume of the reflector causes the reflector difficult to be manipulated, and accordingly results in assembly of the reflector to the enclosure of the LED lamp inconvenient. Furthermore, in order to achieve such desirable light pattern, corresponding parts of the reflector should be optimizedly configured according to different locations of the LEDs, which results in a high cost of the reflector.
What is needed, therefore, is an LED unit which can overcome the limitations described above.